Hey guys. I'm working on debunking an old creationist book (called "Life -- How did it get here? By evolution or by creation?") and I'm trying to debunk these quotes:

"In breeding procedures, breeders usually find that after a few generations, an optimum is reached beyond which further improvement is impossible, and there has been no new species formed which is infertile with its ancestral form, and fertile with other individuals of the same species. Breeding procedures, therefore, would seem to refute, rather than support Evolution. "—On Call, July 3, 1972, p. 9.

Googling for this "on call" magazine suggests it's either a submagazine of the Boston Globe or an "english medical publication".

“Species do indeed have a capacity to undergo minor modifications in their physical and other characteristics, but this is limited and with a longer perspective it is reflected in an oscillation about a mean [average].” Science, "Evolutionary Theory Under Fire", by Roger Lewin, November 21, 1980, p.884.

Now, if these were merely creationist claims, I'd just say "You're wrong. The small changes add up over time." and possibly refer to Talkorigins, which even adresses this specific publication. BUT: the problem is, these are quotes, so they might be quote mines of legitimate scientists, rather than fake scientists talking nonsense. Even Talkorigins just debunks the claim, without explaining what the scientists quoted actually meant by them. Anyone have any ideas?

While I can't tell you anything about the first quote (it's cited exactly like that every time), I can tell you that the second is indeed from an article published in Science: It's behind a paywall though. Note that the article didn't attract a lot of attention, merely two cites...

That being said, I'll address the two quotes quickly:

In breeding procedures, breeders usually find that after a few generations, an optimum is reached beyond which further improvement is impossible

That entirely depends on how "optimum" is defined. It is absolutely true that a cow's udder can't grow to the size of a medium sized car. There are definite physical, chemical and biological laws that constrain the development and evolution of organisms.Just in the same way, you can't very well build a 200m tank, the roads simply won't support it.

and there has been no new species formed which is infertile with its ancestral form, and fertile with other individuals of the same species.

Species do indeed have a capacity to undergo minor modifications in their physical and other characteristics

...and these modifications get passed on, accumulate and, after a few generations, the ancestral population will be very different from the new one.

but this is limited and with a longer perspective it is reflected in an oscillation about a mean [average].

As above, simply horseshit.

I have to temper the above: All of this would probably be true if there were absolutely no selective pressures. Neither natural selection, artificial selection, sexual selection, no gene drift... only stabilizing selection.

While conditions for stabilizing selection might occur every now and then, I suppose you'd be hard pressed to find examples where the conditions lasted for a few million years.

"Sometimes people don't want to hear the truth because they don't want their illusions destroyed." ― Friedrich Nietzsche